Process and apparatus for cracking and separating gasoling stock from petroleum oils



Feb 7, 1933. J, 3, BLACK 1 89345 PROCESS AND APPARATUS FOR CRACKING AND SEPARATING GASOLINE STOCK FROM PETROLEUM OILS Filed Oct. 20. 1926 Patented Feb. 7, 1933 PATENT OFF! JOHN C. BLACK, OF DESTREHAN, LOUISIANA, ASSIGNOR TO GASOLINE PRODUCTS b COMPANY, INC., 013 WILMm'GTON, DELAWARE, A CORPORATION OF DELAWARE PROCESS AND APPARATUS FOR CRACKING AND SEPARATING GASOLINE PETROLEUM OILS This invention is directed to a process of cracking oil, particularly iii a process of cracking oil under pressure.

When oil is heated to its cracking tem perature, it is decomposed into fractions lighter than those present in the original oil. The amount .of decomposition at any temperature is proportional to the time duringwhich the oil is maintained at the cracking temperature. In cracking oil under pressure at any given temperature, it is obvious that a point is reached in the decomposition of the oil when the concentration of the light fractions in the oil impart to the oil a vapor pressure at the temperature which may be equal to, or even greater than the imposed pressure on the oil. When this imposed pressure is exceeded, generation of vapor results.

In operating a cracking process in. the liquid phase, where oil is passedthrough tubes under pressure suflicient to maintain this liquid phase, this vaporization in the cracking system is undesirable. .It is an object of this inventiomtherefore, to increase the amount of decomposition; that is, to increase the length of time during which the oil may be heated and decomposed without generating a vapor pressure greater than the imposed pressure on the oil.

In cracking an oil, as stated before, only part of it is decomposed. It is usual in cracking processes, to separate the decomposed oil into a light'fraction-which constitutes the usual gasoline fraction, and to'separate from the cracked oil a fraction consisting in the main of undecomposed oil, and to recirculate this uncracked oil for further treatment in the cracking system. I have found it desirable to eliminate from my charging stock any light fractions, since these light fractions are refractory-and do not decompose at the temperatures usuallyv employed to decompose the charging stock. They act merely'to absorb heat and to augment the vapor pressureof the oil, thus limiting the amount of decomposition to which the charging stock may be subjected. The

invention will be better understood by referring to the accompanying drawing which shows a cracking system in conventional s'rocx' mu 7 Application filed October 20, 1926. Serial No. 142,999.

13 is a line connecting exchanger 8 with evaporator 14. 13 is a valve in line 13. 15 is a fractionating tower connected to evaporator 14. 16 are bubble trays in said tower. 17 are bubble trays in evaporator '14. 18 is an analyzer. 19 is a vapor line connecting tower 15 with condenser 20. 21 is a lookbox connected to condenser 20. 22 is a condenser run-down line connected to condenser receiving tank 23. 24 is a gas vent connected to lookbox 21. 25 is a trap in tower 15. 26 is afiondensate line connected to trap 25 and liquid seal'27 which is connected with still 29 by means of line 28. 30 are steam coils in still 29. 31 is avapor line exiting from still .29 and connected to condenser 32. 33 is a lookbox connected to condenser -32. 34 is a evaporator Hand to pump 40. 42 is a line connecting pump 40,,with heat exchanger 6. 43 is a line connecting heat exchanger 6 with cooler 44. 45 is a line connecting cooler 44 with the residuum tank46. 47 is a line connected to still 29 for removing unvaporized residue from still 29. 48 is a. tank for collecting oil issuing from line 47; 47 is a valve in line 47-. Y 49 is a line connecting tank 48 with line 3. 49 is a valve in line 49. 50 is ajby-pass line connecting line 7 with line 9.

. 50' is avalve in line.50; 51 is a pyrometer in coil 10. 52 is a pyrometer at the exit1 of coil 10. 53- is a pressure "gauge situated in line 13'before valve 13'. The operation of throu h line 26, seal 27, and line 28 into still the system is as follows:

is pumped by pump 4, by proper manipula- 5 tion ofvalves 49' and 2, through line 3, line 5 by proper regulation of valve 5', and through heat exchangers 6 and 8 into coil 10 situated in furnace 11. In this furnace the oil is heated up to its desired cracking tem- 10 perature as indicated at point 51. From then on its endothermic heat of the cracking reaction is supplied inthe rest of coil 10. Although the system is shown as consisting of one coil in a single furnace, the coil 10 may be divided into two coils, the oil being heated *to the-cracking temperature in onecoil and maintained at the cracking temperature in the other coil, in which other coil the endothermic heat of the cracking reaction is suplied. The heating of the coil is controlled y means of pyrometer 52; that is, the oil is so controlled that the temperature as shown by 52 shall be at least equal to the chosen cracking temperature. The oil passes through heat exchanger 8 where it is partially coole In order to control the cooling of this oil the by-pass 50 is so operated as to pass the required amount of cold oil through exchanger 8. The oil issuing from exchanger 8 through line 13 has its pressure relieved by means of valve 13. The pressure imposed by pump 4 is such as to maintain the oil in coil 10 in liquid phase, that is, the pressure is sufficient to overcome any substantial vapori- 5 zation in the coil. This pressure/is read by .gauge 53. The oil with its pressure relieved is subjected to evaporation by contained heat in evaporator 14. A small amount of steam maybe introduced into evaporator 14 merely to msure proper vaporization. The vapors pass through bubble tray 17 where any entrained oil is separated out. Vapors free of entrained oil pass through plates 16 in bubble tower 15 where the oil is fractionated by the aid of an oil introduced by line 38 into the bubble trays, as will be disclosed later. This fractionation is also controlled by regulating analyzer 18. The vapor issuing through 19 1s crude gasoline, usually termed pressure distillate. This is condensed in condenser 20, the condensate passing through lookbox 21 and line 22 is collected in tank 23.

Uncondensed gases pass through the gas vent 24. The condensate collected in trap 25 contains fractions composed of the heavier ends of the gasoline fractions, and gas oil. This fraction is not entirely suitable for recirculation in the cracking system, in view of the fact that it contains those fractions lighter than gas oil which are refractor and will not crack at the temperature at which gas oil will crack, and will act merely to build up the vapor pressure of the oil in the coils and thus limit the cracking to which the stock may be,

subjected. This fraction is therefore passed in a series of perforated coils in still 29. The -vapors generated are removed through line 31, condensed in condenser ,32, and the condensate passed through lookbox 33 line 34 to tank 35. The uncondensed vapors'are removed through gas vent 33'. The condensate collected in 35 is recirculated by proper manipulation of valves 36' and 38', through line 36,and pump 37 n this stilltheoil is distilled by aid of A combined stock from tank 48 and tank 1 steam coming through line 30 which. ends\ and line 38 to thetower 15 as mentioned before. In passing down through thistower, this condensate acts as a reflux agent and is itself vaporized to remove any lighter gasoline fractions which pass out with the gasoline resent in the oil injected via line 13. The a resi Hum separated in the evaporator 14 is removed via line 39, pump 40, through line 42, and then passes into heat exchanger 6in heat exchange with the incoming oil then passes through line 43 and is cooled in cooler 44 and passed through line 45 to a storage tank 46. The unvaporized still bottom in still 29 is gas oil free of the lighter fractions which would give trouble in cracking. It is removed via line 47 and valve 47 and sent to storage tank 48, from which it is then picked up, as I have described above, by line 3and-recirculated through the cracking system or may be sent to storage if desired. The intermediate fraction removed as vapor throughline' 31,

as disclosed above, is separated into two fractions, the gasoline fraction and a heavier fraction. Therefore, the amount of condensate'present in tank 35 will always be substantially constant in quality and there will be accumulationof condensate in this tank. As a specific example of this operation. the fol vlowin'g'may be given:

' G'as oil which constitutes the charging stock in tank 1 is passed .through exchangers 6 and 8, raised to a temperature in the neighborhood of 500 F. to 600 F., passed through coil 10 and raised to a temperature of about 840 "F. and maintained at. this temperature for a iqo period of about twenty minutes to cause a cracking of the oil. coil 10 is then passed through exchanger 8, where it is cooled down by the proper manipulation of the valves 50 and 5 to about 700 F. The pressure imposed upon the oil is such that the terminal gauge 53 shall show approximately 1000 pounds. The oil is then released to atmospheric pressure in evap= orator 14 where it is distilled and the residuum removed .through 39. This residuum consists of about 10% of the charging stock. The vapors rising through tower 15 are fractionated with the aid of reflux introduced through line 38. The final condensate collected in tank 23 represents about 25% of the charging stock. The condensate collected in trap 25 Which represents about 65% of the The oil issuing from i about of the charging stock. The oil separated in still 29 is a gas oil of approximately the same boiling range as the original gas oil and represents about 55 per cent of the charging stock. The uncondensed gases 10 removed from 24 represents about 2% or 3% of the charging stock. As will be observed, this process will form an improved recycle stock, free of light fractions which act merely as a detriment. It will also be observed that these light fractions usually present in the recycle oil are not lost,

but are separated into their constituent parts that is, the gasoline fraction and the gas oil fraction.

The above is not to betakcn as limiting my invention, but merely as illustrative of the best manner of carrying out my invention, which I claim to be: 1. An apparatus for cracking oil, compris- 25 ing a furnace, tubes in said furnace, an evaporator, means for circulating oil through said tubes to said evaporator, fractionating tower connected to said evaporator, means for removing condensate from said tower, means for removing uncondensed vapors from said tower, a still, means for passin said condensate from said tower to said still, aliquid draw-off from said. still, means for passing liquid from said draw-off to said 5 tubes, means for removing vapors from said still, means for condensing said vapors, means for recycling condensate thus formed to said tower.

2.'A process (if cracking petroleum oils 40 for the production and separation of gasoline boiling point stock, comprising, passing a petroleum oil through a heating zone under a pressure sufiicient to prevent any substantial vaporization therein at'a temperature suflicient to crack the same, reducing the pressure and introducing the heated cracked oil into a i fractionating zone, vaporizing the gasoline boil ng pointstock together with a higher boiling distillate, separating, condensing and so collecting the major part of the gasoline boiling point stock'from said higher boiling'distillate by fractionating and washing the said vaporized oilswith a re-distilled fraction of said higher boiling distillate gontaining gasoline boiling point stock, thereby re-vaporizing, separating, condensing .and collecting the major portion of thesaid gasoline boiling .point stock contained by said wash oil passing the said higher boiling distillate commingl ed I .60 with the unvaporized wash oil into a distilling zone where thegasoline boiling point stock retained by the wash oil and a fraction of the 'higher boiling distillate are vaporized, con- ,densed, collectediand returned to the frac- Mtionating zone as a wash oil; removing the unvaporized fraction from the distilling zone and returning the same to the heating zone for recracking together with fresh oil.

3. A process for fractional separation of gasoline boiling point stock from cracked petroleum oils, comprising, passing a petroleum oil through a heating zone under high superatmospheric pressure wherein said oil is heated to a cracking temperature, introducing the heated cracked petroleum oil into an ei'aporating zone, connected to a fractionating zone, at a pressure less than that employed in the Cracking operation, vaporizing the gasoline boiling point stock together with a. higher boiling distillate, separating, condensing and collecting the ma or part of the gasoline boiling point stock from the higher boiling distillate, by fractionating and washing the said vaporized oils with a re-distilled fraction of said higher boiling distillate containing gasoline boiling point stock, thereby re-vaporizing, separating, condensing and collecting the major portion of the said gasoline boiling point stock contained by said wash oil; passing the said higher boiling distillate commingled with the unvaporized washcoil into a distilling zone where the gasoline boiling point stock retained by the wash oil and a fraction of the higher boiling distillate are vaporized, c0ndensed,,collected and g returned to the fractionating zone as a wash oil; continuously removin the unvaporized fraction from the said distilling zone and returning the same to the heating zone for recracking together with fresh oil.

4. The process of treating hydrocarbon oil comprising the steps of cracking said oil under superatmospheric pressure, subjecting the heated oil to evaporation by relieving the pressure thereon and fractionating the resulting vapors, recovering a pressure distillate, a residual bottom, and a reflux condensate, subjecting the reflux condensate to distillation by applied heat thereby separating light overheadvapors and a bottom therefrom, subjecting said light vapors to condensation to produce cooled overhead distillate, recycling the stripped bottom as a re-charging stock to the cracking stage, recycling said cooled overhead distillate as a reflux liquid for fractionating vapors obtained b relieving the pressure on the cracked pro ucts.

comprising the steps of cracking said oil un- I derj'superatmospheric pressure, subjecting the cracked products to evaporation and fractionatingthe resulting vapors, recoverin a pressure distillate, a residualbottom, an a reflux condensate, separately stripping the reflux condensate of its lighter endsby distillation and recoverin light vapors and a bottom therefrom, pro ucing light condensateby condensing said light vapors, recycling the stripped bottom as a recharging stock to i the cracking stage and introducing said light wcondensate directly into the vapors obtained by evaporatin the cracked oil as a cooling reflux to contro fractionation of these vapors. 6. A process for treating hydrocarbon oil 5 comprising the steps of cracking said oil under superatmospheric pressure, subjecting the cracked products to evaporation and fractionating the resulting vapors, recovering a pressure distillate, a residual bottom, and a 1 'refiux condensate, stripping the reflux condensate of its lighter ends by distillation before substantial cooling of said condensate, to produce light vapors and a bottom therefrom, producing "light condensate by condensing said light vapors, recyclin the stripped bottom as a recharging stoc to the cracking stage and returning said light condensate stripped from the reflux condensate to the fractionating stage as a cool refluxing liquid. 2 7. A process for treating hydrocarbon oil comprising the steps of cracking said oil un-' der superatmospheric pressure, subjecting the cracked products to evaporation and fractionating the resulting vapors recoverin' a pressure distillate, a residual bottom, an a reflux condensate, stripping the reflux condensate of its lighter ends by applied heatdistillation before substantial cooling of said condensate to produce light vapors and a bottom therefrom, producing-light condensate by condensing said light vapors, recycling the stripped bottom as a re-charging stock to the cracking stage and utilizing the said light condensate as a cool control reflux liquid in 5 the fractionating stage. I

1 8. A process 1n accordance with claim' 7- wherein said 1i ht condensate is heavier than said pressure distillate. l 9. A process in accordance with claim 7 40 wherein said hydrocarbon oil is gas oil, said pressure distillate is gasoline, said light con- 4 densate comprises a fraction intermediate between gasoline and gas oil and *said bottomis of approximately the same boiling range as said gas oil first mentioned.

In testimony whereof I'aifix my signature.

JOHN C. BLACK. 

